Asserbo Castle was founded by Bishop Absalon in the 1100s as a monastery for monks of the Carthusian Order. The castle was taken over first by the King around 1560 and in subsequent centuries by drifting sand. The castle was liberated from the sand in two phases: initially by King Frederik VII in 1849 and then by National Museum excavations in 1972.
References:Visby Cathedral (also known as St. Mary’s Church) is the only survived medieval church in Visby. It was originally built for German merchants and inaugurated in 1225. Around the year 1350 the church was enlarged and converted into a basilica. The two-storey magazine was also added then above the nave as a warehouse for merchants.
Following the Reformation, the church was transformed into a parish church for the town of Visby. All other churches were abandoned. Shortly after the Reformation, in 1572, Gotland was made into its own Diocese, and the church designated its cathedral.
There is not much left of the original interior. The font is made of local red marble in the 13th century. The pulpit was made in Lübeck in 1684. There are 400 graves under the church floor.